Bed-wetting has no magic timetable Patterns: Parents and children should understand that bladder control does not come automatically with a certain age.

Parents often want to know when they should start worrying about bed-wetting. Most children are able to stay dry during the day by age 3, but there is no predictable time for success at night. Though some see it as a problem if a child has not stopped wetting the bed by the age of 5, many children are not "ready" to stay dry when we expect them to.

Some children have an immature bladder, which leads to difficult night control. There are also children whose sleep patterns are immature. Their arousal patterns in light (REM) sleep are not well developed enough to alert them to get out of bed to use the bathroom.

These children need to develop on their own schedule, which must be respected. Pressure from parents or peers can add guilt and feelings of inadequacy, but they won't change the child's developmental patterns. Parents of such a child need to be patient - and they should help the child understand the reason for his "lack of success." Otherwise, it can lead to a poor self-image - one of failure.

Boys are more likely to be bed-wetters than girls. Some of this may be due to anatomical differences, but it surely is also due to differences in societal expectations and to expectations young boys have of themselves.

By the age of 5, a boy who is a bed-wetter is likely to feel pressure from his peers. He will try to hide his "defect." Denial will set in, and he will refuse to share any of his feelings of shame or failure.

Parents who see this situation developing should first consult their pediatrician to rule out physical reasons. Once that has been done, parents should reassure the child that he is OK and then do all they can to lighten up on pressure.

Above all, staying dry at night must become the child's goal. Parents must relax the urgency they feel. If this seems impossible, they might consider turning to a counselor or someone who can help figure out how to defuse undue pressure on the child, as well as the parents' own involvement.

The parents' task is to listen to the child's feelings and to support his efforts to stay dry. If there are issues of poor self-image, of psychological immaturity or of self-devaluation, they must be addressed.

Questions or comments should be addressed to Dr. T. Berry Brazelton, care of the New York Times Syndication Sales Corp., 122 E. 42nd St., New York, N.Y. 10168. Questions of general interest will be answered in this column; Dr. Brazelton regrets that unpublished letters cannot be answered individually.

WHAT PARENTS CAN DO TO HELP THE CHILD

When the child is ready, here are some other steps I recommend to parents:

* Ask your child to hold onto his urine a bit longer during the day, to help increase bladder control.

* With the child's permission, you can wake him before you go to bed. At that point, he must take control, or it won't work. Don't carry him to the pot.

* An excursion to buy a "nighttime pot" for the child's bedside, one that can be painted with luminous paint, could become a symbol of parental support. Then, you can wake him up to use it. This must be supportive and not pressured. No matter how close the real toilet is to his bed, this symbol can be meaningful.

* An alarm clock by the bed to wake the child at 2 a.m. could help when he's ready. Before he is ready, it is unnecessary pressure that will work the wrong way.

* Subtle efforts to reassure the child and support him about his success during the day can shore him up for the night. But, if overdone, they can also make him self-conscious.

* When your child wants to talk, you can discuss his feelings, the pressures on him and the fact that his bladder may need to grow up and that it may take a little while for him to learn to wake up in time. If this is a real dialogue, it can be reassuring to him.